The paradigm for prior art orthopedic plates has involved drawing an image of the plate to suit a general outline of a site where the plate was intended to be implanted. Thus, the plate began its conception as a two dimensional representation. The final manifestation was crafted from metal and often had no, or very crude profiling in the Z direction. As this corresponded poorly with the surface of the bone that it was designed to fit, the plate was made relatively thin to allow the surgeon to contour the plate before implantation. In addition, the plate was made somewhat thin so that it could be fixed in place on the bone and that the bone itself would provide the basis of the final sculpting. This paradigm presents several problems for the attending surgeon. First, the surfaces of bone are far from flat, and the smaller the bone, the greater the relative contouring that the surgeon had to accomplish during the surgery. Second, while intact cadaveric bone can provide a basis for contouring a flexible plate, this idea is less successful with bone that has been fragmented, and the worse the break, the more difficult the reconstruction. The present invention provides the means to design orthopedic plates that can be used as the scaffolding for reconstruction of broken or deformed bone or for bones otherwise requiring orthopedic attention. The means of accomplishing the design of such a plate is the use of imaging studies of human anatomical samples to construct a generalized three dimensional solid model from which one or more computer models or resin samples can be made and which forms the basis for the three dimensional design of a corresponding orthopedic plate which is easily subject to subsequent development and design review.
In particular, the present invention uses a high-resolution model of the distal radius based on imaging studies of human anatomical samples. Samples of 16 cadaveric distal radii were harvested and high-resolution CT scans of the samples were collected and the CT data were converted to solid-part 3D models. Measurements from the cadaveric samples, CT slice images, and 3D solid part models were compared to verify the accuracy of the models. Individual models were then overlaid to create three sizes of composite models of the distal radius. In addition, simple plastic models of the samples were created using a 2-step casting process. This provided a physical correlation to the digital model for more accurately fitting the prototype plates. The current invention provides the additional advantage that the digital model created can be used for specific description of the distal radial anatomy, as well as the design and testing of fracture fixation hardware and surgical approaches and techniques since the resin castings that are created are characteristically hard and are difficult to drill or otherwise physically test.
The process described here may also be used to create similar models of other bony structures for similar end uses, including specifically small bones (i.e., below the elbow or knee, or the clavicle) and joints such as the calcaneus, the tarsals, and metatarsals, the carpals and metacarpals, the tibia, the fibula, the clavicles; long bones such as the humerus, femur, and the ulna; the vertebrae, and the pelvis and the bones of the skull.
Fractures of the distal radius are among the most common seen by orthopedic surgeons, with estimates of annual incidence ranging from 9 per 10,000 to as high as 120 per 10,000 in different populations. However, while several authors have utilized CT of the distal radius for specific diagnoses, no high-resolution model of the distal radius articular surface, epiphysis, and metaphysis based on data acquired from human materials has been reported in the literature.
In order to construct an accurate model of the distal radius, high-resolution, minimal-noise CT scans of distal radii were acquired from an immediately available selection of sixteen cadaver samples. The data from the CT scans were then used to create a composite digital model of the distal radius, which represents a composite of the models of the individual bones. This model is used in accordance with the present invention to describe in depth the typical geometry of the distal radius for design of orthopedic hardware and for injury management including surgical technique. Subsequently, the models drawn in cross section at a defined interval and a plate is constructed in a process termed “lofting” in which a cross section of plate is added at the surface of the bone (assuming to begin with that the section is rectilinear) and the plate sections are aggregated to construct a plate form which blankets the graphical bone model at its surface and which is subsequently formed to a outline that is appropriate to a particular indication. Alternatively, the outline can be selected first and the plate form can be cut in the outline shape when it is designed. In any case once the form is designed and the outline is selected, there is a plate shape design which can be used with the bone model to place fixation means, which can include all of the varieties of fixation, including but not limited to bone screws and pegs, including locking and unlocking varieties of each, K wires, wires, tensioning devices, bone anchors and adhesive. Once fixation means are added, there is plate prototype design that can be studied through computer analysis to accommodate various considerations, such as typical fractures or bone deformities, complications, problems of approach including soft tissue involvement, and loading that the implant or plate typically withstands. This easily enables the involvement of medical experts who can review electronically transmitted proposals and can comments on considerations such as the ability to capture typical fragments, fixation concerns such as impingement of fixation means on the construct or interference with soft tissue, and other issues involving ease of surgical approach and implantation. Further, it is of great assistance to make physical-models of plate and bone to allow medical advisors to play with placing the plate on the bone and suggest further advantageous adaptations. While the resin that is often used for modeling is too hard to allow for a simulation of implantation in bone, a resin model can be used to make a female mold that can be used to make a further model of artificial bone so that the medical personnel can play with the entire bone/plate/fixation construct to make additional suggestions that are incorporated into the final plate design. Thus, the method of the present invention allows far more intensive study of many aspects of the plate/bone/fixation construct enabling the possibility of better fit, ease of surgical use, better standardization for the relevant population, and better fixation and reduction eliminating possible causes of future complications, including misalignment and attendant joint pain and malfunction, and arthritis.